38th LaMer Special Seminar “What can we learn from the chemical tracers? – Material transport between the marginal seas and the Kuroshio -” was held on February 4th, 2020.
We deeply appreciate that we had lots of attendance. 

Date: February 4th, 2020
Time: 10:00 – 11:30
Venue: Meeting room #674, Science Research Bldg 1

■Lecturer: Prof. Jing Zhang
                 Graduate School of Science and Engineering, University of Toyama

■Abstract: Marginal seas in the western North Pacific and western boundary current area are constantly or intermittently exchanging energy and materials between land and open ocean. A large amount of nutrients is transported between the boundary area of the East China Sea (ECS) shelf region and Kuroshio, however, it is difficult to clarify the various sources solely by estimating the potential temperature (PT) and salinity. Chemical tracers e.g. rare earth elements (REEs), Nd and Cs isotopic compositions (εNd, 137Cs) are suitable and conservative as water mass indicators, and are excellent tools for classification and analysis of multiple water masses while coupling with salinity and temperature, particularly where there is complex water structure. The estimation of the mixed four water masses is, Mixed Shelf Water (MSW), Kuroshio Surface Water (KSW), Kuroshio Tropical Water (KTW), and Kuroshio intermediate Water (KIW), with KIW and KTW accounting for 39±14% and 49±18%, respectively, of the central ECS shelf bottom water (Zhang et al., 2018). Using Nd concentration and εNd. three end-member models indicate that approximately 10% of the CDW (Changjiang Diluted Water), 28% of the YSW (Yellow Sea Water), and 62% of the Kuroshio Water enter the Sea of Japan while approximately 6% of the MSW discharges into the adjacent areas of the Northwestern Pacific (Che and Zhang, 2018). To clarify the nutrient transport through the Tsushima Strait from the North Pacific to the Sea of Japan, 137Cs originated from the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident is used as a direct indicator. A maximum 137Cs in the Luzon Strait area, ECA and Tsushima Strait, were observed in the same water mass, with the similar temperature (15-17C), salinity (34.60-34.75) and density (sq, 25.2-25.7), which is recognized as Subtropical Mode Water (STMW). KIW, gradually located at 400m in Luzon Strait and up to 150m water depth at the Tokara and Tsushima Straits, is rich in nutrients. As a result, KIW (STMW) transports about 10% of nutrients into the Sea of Japan in total flowing through the Tsushima Strait.  
Keywords:
rare earth elements, εNd, 137Cs, nutrient transport, Luzon Strait, East China Sea